Volvo recently announced the development of several gasoline engines that can be added to its electric vehicles to increase their range - the distance travelled between fill-ups. Known as "range extenders," the engines are similar to what's found in the Chevrolet Volt, and help boost the range of Volvo's C30 Electric prototype by more than 600 miles.

Although Volvo has yet to decide on a single range-extending option to supplement the C30 Electric's battery life, the automaker says that it's testing three possibilities. Technical Concept 1 adds a 60-horsepower, three-cylinder rear-mounted engine and 10.5-gallon fuel tank to the C30 Electric, augmenting the hatchback's 111-horsepower fully electric motor. That gives the C30 Electric around 700 miles of total range, with 68 miles coming from the electric motor and 620 coming from the car's range-extending gasoline engine.

Technical Concept 2 is geared towards performance over fuel economy. It features a 190-horsepower turbocharged version of the rear-mounted three-cylinder found in Technical Concept 1. Volvo says Concept 2 can also reach 620 miles using its gasoline engine, but the higher-performance setup brings the range of its electric motor down to just 45 miles.

Due to a two-stage automatic transmission and 40kW generator, Technical Concept 3 is more complicated than Volvo's other offerings. But this concept allows the electric and gasoline motors to work together. The electric motor propels the car up to 30 miles per hour, and the gasoline engine takes over at higher speeds. The result is a total range of around 650 miles.

"This is an exciting expansion of our increasing focus on electrification," said Derek Crabb, vice president of powertrain engineering for Volvo cars. "Battery cost and size mean that all-electric cars still have a relatively limited operating range. With the Range Extender, the electric car has its effective range increased by a thousand kilometers."

Despite many automakers promising electric cars in the near future, just two manufacturers - Nissan and Chevrolet - have brought mainstream examples to the market. While the Nissan's Leaf is fully electric, the Chevrolet Volt already makes use of a range-extending gasoline engine, giving it a total range of nearly 350 miles after its 35-mile electric motor runs out of power. While Volvo plans to start rolling out electric vehicles in early 2012, the automaker says they'll be restricted solely to European test fleets for now.

This image is a stock photo and is not an exact representation of any vehicle offered for sale. Advertised vehicles of this model may have styling, trim levels, colors and optional equipment that differ from the stock photo.